Arduino Teaches Old Coder New Tricks

The Project

Now that I had invested a lot of
time into learning the Arduino system and the Atmel microcontrollers, I
wanted to take the next logical step: move a design from the breadboard
to a printed circuit board. Some interesting projects exist in this
area, such as Fritzing, which is designed to facilitate doing exactly that.
It's a
clever project and you should check it out, but I
took a different path—using the gEDA open-source Linux software suite
for printed circuit development.

I looked at my inventory of parts and started thinking of what I could
create that wasn't already readily available. I settled upon the LCD
display. The displays being used in Arduino projects were interfaced
with a lot of I/O pins and code space, neither of which are in great
supply on the Atmel chips. I felt that if I could create a same-size
daughter board that I could attach onto the back of the display and put
the smarts into the board that would communicate with the LCD display
via an ASCII serial interface, I would have something
useful that didn't exist in the marketplace in an affordable form. This
is commonly called a serial LCD.

Being somewhat of an old-timer, I spent a lot of time using and coding
for the DEC VT100 display terminals upon which the ECMA-48/ANSI X3.64
standards are based. I felt that if I coded the daughter board to turn an
LCD display into a tiny, affordable DEC-VT100, I would have something
reasonably unique and useful. Serial-driven LCD displays do exist, but they
typically have proprietary protocols, and some are rather expensive. As far
as I have been able to determine, there exists no open-source (software
and hardware) serial LCD display with VT100 protocol. I found my project!

Gathering the Parts

I selected parts for the VT100-LCD project, such that the parts would be
as affordable as possible. In fact, I purchased all the parts from two
sources, eBay and Digi-Key, based on cost.
Table 1 shows the required materials to build one
vt100lcd. Costs are shown on a per-item basis; however, I purchased most
of these items in quantities of five or more.

Table 1. vt100lcd Parts List

Part

Qty

Source

Cost

1602 HD44780 LCD

1

eBay seller (China)

$2.95

Atmel ATtiny84

1

Digi-Key ATTINY84-20PU-ND

$3.01

Switch, tactile FSM4JH

1

Digi-Key 450-1650-ND

$0.80

Socket, IC, 14-pin

1

eBay seller (USA)

$0.15

Header, 1X20, Female, 2.54mm

1

eBay seller (China)

$0.39

Header, 1X40, Male, 2.54mm

1

eBay seller (China)

$0.20

Resistor, 330 ohm, 1/4W

1

eBay seller (Thailand)

$0.02

Resistor, 10k ohm, 1/4W

1

eBay seller (Hong Kong)

$0.02

Pot, trim, 5k, RM-065

1

eBay seller (USA)

$0.30

Capacitor, .1uf, ceramic disc, 50V

1

eBay seller (Hong Kong)

$0.05

Transistor, 2N3906

1

eBay seller (Thailand)

$.01

Diode, 1N4148

1

eBay seller (Thailand)

$.01

Total:

$7.91

Optional Parts

Commercial PCB

1

Panel Aggregator

$7.43

Capacitor, 22pf, ceramic disc, 50V

2

eBay seller (USA)

$0.40

Crystal, 20MHz, ATS200-E

1

Digi-Key CTX1105-ND

$0.64

Schematic Design

To design the circuitry for the VT100-LCD, I chose gschem of the gEDA
Project by http://geda-project.org. This suite includes not only the schematic
design program but also a PCB layout program, as well as various helper
programs. A number of schematic/PCB design software programs exist, but I'm
focusing on the open-source software of the gEDA Project
by geda-project.org here. Other open-source projects that run on Linux,
include KiCad, as well as several commercial products, the most popular
of which is Eagle PCB by CadSoft, which runs pretty well under WINE.

gschem is fairly straightforward, and many functions are intuitive, but
a few, useful but arcane commands necessitate printing
out a cheat sheet (hey, I'm getting older and I can't memorize all
of those keystrokes). Yes, although gschem is a GUI program,
useful keyboard shortcuts appear nowhere in the GUI's menus. This
is especially true of the PCB layout program that I discuss later.

The process consists of inserting electronic component symbols into the
schematic drawing either from the built-in library or from your private
library and then connecting the pins by drawing traces. I highly recommend
reviewing the gEDA Project's on-line documentation before starting your
own schematic. There are a few tutorials on the Web about using the
gEDA suite, and Stuart Brorson wrote a tutorial article in the November
2005 issue of Linux Journal (see Resources).

I created two versions of my VT100-LCD project: one using the eight-pin
ATtiny85 microcontroller and another using the 14-pin ATtiny84
microcontroller. The schematic for the ATtiny84 microcontroller version
is shown in Figure 2.

It didn't take very long to remove the mental cobwebs and get into the elegant simplicity of the Arduino Project. Years ago, when I built microprocessor projects, the underlying system code always was the problem. Before I actually could write my application, I had to develop or adapt systems-level code to interface the application-level code with the underlying hardware. Cleaners London